The following description relates generally to a hair-line processing. In on implementation, sheet metal is finished by continuous hair-line on its plane and curved surface, using an apparatus and a method for finishing by continuous hair-line on the same.
Typically, metal materials have intrinsic metallic luster, high-quality external impression, high strength and durability, distinguishing them from other materials that are less continuously and widely used. Metal materials have been used, of late, as sheet metals forming exterior casing parts of mobile communication terminals, i.e., cellular phones and personal digital assistants. In other words, formed sheet metals are employed as materials for use in casings and housings of hand-held electronic products.
Metal processing such as brushing or polishing of the metal surface may provide the intrinsic metal gloss, but such processing suffers from a shortcoming that a simple metal luster may cause a monotonous feeling to a user. Particularly, for products such as mobile communication terminals that attach importance to exterior designs, surface finishing or processing methods for sheet metals have been developed to cater to a variety of consumer demands amidst decorating the exterior appearance with sheet metals.
One such method is a sheet metal developed to generate a decorative effect by forming straight fine hairlines on the surface. The hairline surface finishing is designed to form straight fine hairlines on the surface of a smooth-polished sheet metal performed by steel-brushing or polishing to provide a decorative beauty to the exterior appearance, thus removing the monotonous metallic luster.
The hairline finishing typically performed by manual works that employ rotating sandpaper or steel brushes suffers from shortcomings that many labor hours and low productivity are involved. Another shortcoming is that a space between the hairlines and each length of the hairlines varies responsive to skill and function of a worker to make it difficult to maintain a constant quality level.
Yet another shortcoming is that it is very difficult to process a curved surface of a sheet metal although it may be possible to process the hairlines on a plane surface of the sheet metal using the conventional hairline finishing method, considering that there are a curved surface and a plane surface mixedly arranged on an exterior surface of the mobile communication terminal. Particularly, it is difficult to form continuous uniform hairlines from one plane surface to another plane surface through a curved surface when the curved surface exists between said one plane and said another plane surface.
Meanwhile, hairline surface finishes may be erased by pressing work in the course of pressing process, a distance between hairlines may be worn out by stretching of the curved surface portions, or external appearance may be damaged by efflorescence that is characteristic to metal materials, when hairlines are first processed on one surface of a sheet metal and the sheet metal is processed to have a curved surface through press process including post-operation.
As a result, there have been cases where a hairline surface finish is carried out only on a partial plane surface, where the hairline surface finish can be performed in case of a sheet metal, where a plane surface and a curved surface are mixedly available, and the hairline surface finish is discarded on the curved surface portions. In other words, the hairlines are formed only on the plane surface of a sheet metal where both the plane surface and the curved surface exist at the same time, but a sheet metal having continuous hairlines even on the curved surface has yet to be developed.